The rapidly increasing adoption of mobile communications facilities, such as cellular telephone systems, has led to a huge and growing demand for the associated user devices, such as mobile telephone handsets and other mobile stations (MS). Accurate control of the output power of these devices is important both for the quality of service provided by the devices and for minimising potential interference caused to other users of the system. To this end, it is essential that the output power of every device is fully characterised, at multiple power levels, by the manufacturer before shipment to ensure the device is compliant with prescribed performance characteristics. Equally however, the manufacturers desire that these tests should be accomplished as quickly as possible, to minimise delays they introduce into production timescales.
In the case for example of the 8-PSK modulation format used in the Enhanced Data rates for GSM Evolution (GSM/EDGE) system, the relevant European Telecommunications Standards (3GPP TS 05.05, 45.005, 51.010, 11.21 and 51.021) provide for measurements of a variety of parameters including output power. The GSM/EDGE system employs Time Division Multiple Access (TDMA), in which a mobile station is allocated a precise time interval in which to transmit. The short transmission occupying this interval is called a burst. In the GSM/EDGE system a burst can be modulated either with Gaussian Minimum Shift Keying (GMSK) or with 8-Phase Shift Keying (8-PSK). GMSK is a constant-envelope modulation scheme, which means the mobile station transmits at a constant power level for the duration of the burst. 8-PSK is a non-constant-envelope modulation scheme, so the mobile station's output power changes during the burst as a function of the modulating data. Furthermore, when modulated with a continuous stream of random data, the average power of an 8-PSK modulated signal will vary from burst to burst. The relevant standards specify that direct determination of 8-PSK power is to be accomplished by averaging the power measured over many bursts. Alternatively, the standards allow for other unspecified techniques which when applied to a single burst can provide an estimate of long-term average power.
Mobile stations are typically capable of transmitting over a range of specified output power levels. They must also be capable of transmitting at all frequencies in their bands of operation. The standards require that output power is measured for all power levels and at the lowest, mid-point and highest frequencies in each band of operation. This typically results in 40 or 50 test points for each operating frequency band. If direct measurements of output power of 8-PSK modulated signal bursts are made, 100 or more bursts would typically need to be measured at each one of these test points.
It is an object of this invention to reduce overall test time by estimating the carrier power, and equivalently, the long-term average power, from measurement of a single burst while complying with the measurement accuracy requirements.